Hello, John_Gio16.
Thank you for posting in Apple Support Communities. We understand that you’re attempting to help your son redeem the app you gifted to him in the App Store. From your screenshot, it looks like you may be trying to locate the gift in the wrong area on your iPhone. The “Redeem Gift Card or Code” link here is where you would manually enter the code from a physical card. When you electronically send a gift through the App Store it will send an email with a “Redeem” link. When you click on this link from the device where you want to download the content it should automatically open the App Store and start the download.
Are you still able to access the email on his iPad? If you are, what happens when you tap the link to redeem here?
If you’re not able to find the app this way, you may be able to resend it. Check out “Resend a gift” here:
Gift apps, music, movies, and more from Apple - Apple Support
Warmest Regards.